Photographic desensitizer



Patented Nov. 2, 1937 UNl'l'ED STATES PATENT OFFICE 2,098,086PHOTOGRAPHIC DESENSITIZER No Drawing. Application July 16, 1936, SerialNo. 90,891. In Germany July 25, 1935 4 Claims.

My present invention relates to photographic desensitizers.

One of its objects is an improved desensitizing solution. Furtherobjects will be seen from the detailed specification followinghereafter.

A good desensitizer should fulfill the following requirements:

1. It should be colorless.

2. It should not be flocculated by the antihalo dyestuff which mostphotographic materials for amateurs now contain.

3. The anti-halo dyestuff should be nullified in the desensitizingsolution, so that the coloring of the bath and possible damage to thephotographic emulsion layer may be avoided.

It has been proposed to use for desensitizing sensitive silver halideemulsions, particularly panchromatic emulsions, colorless water-solublederivatives of anthraquinone or phenanthrenequinone. These compoundshave not, however, been introduced into practice as desensitizers, sincetheir capacity in this respect is far below that of the known bestdesensitizers, especially Pinacryptol green and Pinacryptol yellow.

5 This invention is based on the observation that the desensitizingeffect of water-soluble derivatives of anthraquinone orphenanthrenequinone may be considerably increased by using suchderivative in a solution which contains at least 2 30 per cent of sodiumsulfite, calculated as anhydrous salt. The solution may contain anamount of sodium sulfite up to saturation.

Such a desensitizing solution is equal in its effect to the hithertoknown best desensitizers. It

5 also possesses notable advantages as compared with the knowndesensitizers:

1. The solutions are completely colorless.

2. The desensitizers are not flocculated by the anti-halo dyestufi.

40 3. Owing to the presence of sulfite it is ensured that the anti-halodyestuff will be nullified in the preliminary bath. This makes itpossible for the negative material to be controlled by inspection fromthe first moments development. Moreover,

45 in this manner diffusion of any photographically injurious anti-halodyestuii from the non-curlinglayer and its passage into the photographiclayer is avoided, a mishap which was possible in the case of the oldpreliminary baths.

50 These properties are not united in any of the known desensitizingsolutions. The desensitizing solutions of this invention fulfill in anideal manner all the requirements of the case.

This technical eifect is surprising to the ex- 55 pert, for previousknowledge indicated that the derivatives of anthraquinone orphenanthrenequinone are little suitable as desensitizers and they werenot used as such. It could not be expected that the use of sulfite wouldincrease the desensitizing effect of these bodies for example 5 by 10 to15 times (with a content of 4 per cent of sulfite) for it was known thatsulfite has a weakening effect, and indeed a destructive eiiect, onnumerous desensitizers. It has indeed been found that the desensitizingeffect of derivatives of 10 anthraquinone or phenanthrenequinone is notdiminished in presence of sulfite, but it has not been observed that thedesensitizing effect can be raised by this agent. Thus it was not knownthat by a definite content of sulfite there would 15 be so high anincrease in the desensitizing effect that the action would becomeequivalent to that of the best desensitizers.

Recipes for suitable preliminary baths in accordance with this inventionare as follows: 20 1. Sodium 1-nitro-anthraquinone-7-sulfo nate gram 1Sodium sulfite grams 40 Water cubic centimeters 1000 2. Sodiumanthraquinone-2-sulfonate gram 0.5 Sodium sulfite grams 40 Water cubiccentimeters 1000 3. Sodium 1-chloro-anthraquinone-2-carboxylate gram 0.5Sodium sulfite grams 40 Water cubic centimeters 1000 4. Sodiumanthraquinone-Z-carboxylate gram 0.5 Sodium sulfite grams 40 Water cubiccentimeters 1000 What I claim is:

1. A photographic desensitizing solution which comprises an aqueoussolution of a water-soluble compound selected from the group consistingof an anthraquinone and a phenanthrenequinone, and at least 2 per centof sodium sulfite.

2. A photographic desensitizing solution which comprises sodiuml-nitro-anthraquinone-7-sulfonate, at least 2 per cent of sodiumsulfite, and water.

3. A photographic desensitizing solution which comprises sodium1-chloro-anthra uinone-2- carboxylate, at least 2 per cent of sodiumsulfite, and water.

4. A photographic desensitizing solution which comprises sodiumanthraquinone-2-carboxy1ate, at least 2 per cent of sodium sulfite, andwater.

WALTER DIETERLE.

